With using AFM, measurement of force (force curve) working on a single particle holding electrostatic charge generated at contact with metal target was conducted. As sampl, PS particles with 100 micro-meter in diameter were used, and 8 kind of metal as Al, Au, Cr, Ni, Pt, Ti, Zn, and Zr were used as the target on which every surface was polished and mirror finished. Results can be summarized as follows:
1. First of all, force curve was successfully measured with the method, and the measurement procedure was established.
2. By focusing to “force curve” measurement, not looking at only maximum adhesive force, electrostatic interaction was successfully observed by separating other interactions as liquid bridge and intermolecular force.
3. The force curve attributed to the electrostatic interaction was analyzed by theory with an approximation of disk-to-disk interaction based on image force method. The fact of successful agreement between the observed force curve and theory revealed that the force curve observed can be surely attributed to the electrostatic interaction, and that the amount of charge on the particle and the radius of the charged (contact) area can be estimated from the analysis.
4. The order of magnitude of the measured charge density was 10-2 C/m2, which is much greater than that obtained with “impact charging experiment,” which has been previously studied, as 10-4 C/m2.
5. From the fact, it was concluded that the force curve measurement with AFM can catch the net amount of the charge generated before charge relaxation due to gas discharge takes place.
6. The net charge generated was revealed a good compatibility to the conventional simple condenser model based on metal-to metal contact model with the term of contact potential difference in its order of magnitude.
7. No correlation was revealed for the charge density measured against work functions of metal targets, regrettably.
In the respect, subject left over could be summarized as:
1. More careful experiments and data accumulation, especially in the terms of reproducibility and accuracy, will be required to establish the method in the near future studies.
2. Because the work functions used in the analysis were from literature, it might be necessary to measure their real values practically.
3. Variation of sample particles with different size and materials are interesting and necessary to be addressed.